1. Field of the Invention
The present invention relates to a plasma processing device or a plasma processing method used to process a substrate-shaped sample such as a semiconductor wafer disposed in a processing chamber disposed within a vacuum vessel, by using plasma formed in the processing chamber. In particular, the present invention relates to a plasma processing device or a plasma processing method in which pulse-shaped output intensity, a duty ratio, and a pulse frequency of high frequency power for plasma forming or high frequency power for forming bias potential supplied to electrodes within a sample stage on which the sample is placed are changed over to different values.
2. Description of the Related Art
In the semiconductor manufacture process, dry etching processing is conducted to etch a film structure having a plurality of film layers including a mask layer formed by previously laminating on a top surface of a semiconductor wafer, by using plasma. A plasma processing device, which executes such processing, has the following configuration. That is, the plasma processing device forms plasma by supplying an electric field formed using high frequency power for plasma forming while introducing gas for processing into a processing chamber within a depressurized vacuum vessel. The plasma processing device supplies power from a different high frequency power supply to electrodes disposed in a sample stage within the processing chamber, and forms bias potential over a sample such as a semiconductor wafer placed and held on a top surface of the sample stage. The plasma processing device processes a target film in a film structure on a surface of the sample while attracting charged particles in the plasma to the surface of the sample in the plasma and causing the charged particles to collide with the surface of the sample. With advance of higher integration in semiconductor devices and three-dimensional structures in recent years, improvement of work precision is required of the plasma processing device conducting such dry etching and improvement of etching selection ratio or improvement of high precision control of the etching shape is required of the plasma processing device conducting such dry etching.
For executing such work, it is necessary to optimize a plurality of parameters such as an ion density at the time of etching processing, a radical density, energy of ions incident on a material to be etched, and a density and concentration of reaction products generated by etching reaction on a surface of the target film, in accordance with a material of a film to be processed. These parameters depend upon conditions under which etching processing is executed (such as, for example, a kind of gas, a pressure in processing in the processing chamber, a composition (mixture ratio) of gas including a plurality of elements, a value of the high frequency power for plasma forming, and a value of the high frequency power for bias forming).
In general, when conducting etching processing on at least one specific film, it is conducted to change over to suitable processing conditions every film layer or with the advance of processing even for a layer of the same material and execute processing. Such processing conditions are called recipe. In conventional etching processing of a film structure of a top surface of one sample in a plasma processing device, a plurality of different processing steps are executed consecutively under different processing conditions (recipes). Such processing conditions (recipes) are input to a controller in the plasma processing device as electronic or electric data or information. The controller adjusts operation of a vacuum processing device to implement recipes indicated by input information individually, change over a plurality of processing steps in order, and execute etching processing.
In recent years, a method for improving controllability of the ion density and radical density by pulsating the plasma generation to further optimize the etching processing conditions is proposed. In addition, in order to conduct etching of a high aspect ratio on a multi-layer film structure and a three-dimensional structure, improving the selection ratio by applying pulsated bias and using deposition effectively and suppressing damage by reducing the electronic shading effect are also proposed.
Therefore, a technique for executing processing by using a recipe that causes the high frequency power supply to conduct pulse output in a specific processing step is proposed. For example, if it is suitable to cause the high frequency power supply to conduct pulse output in processing of any material in a case where a multi-layer film including materials of two different is etched consecutively, a recipe that changes over alternately pulse outputs of two kinds is set and the recipe is transmitted to the controller via a communication means. The controller sends an instruction signal to regions in the plasma processing device in accordance with the recipe, and etching processing is conducted.
In such a recipe that changes over pulse output modes of two kinds, a shift from former one in two processing steps that are consecutive before and after to latter one is conducted. In a case where a deviation exceeding an allowable range occurs at the time of changeover of the output intensity, duty ratio, and pulse frequency in the shift, power is output with an output intensity that is longer than and higher than the setting value. Here, the duty ratio is a ratio of a period for which a value of a specific level (magnitude), especially a large value is output, to one repetition period of the pulse output.
FIG. 1 is a graph schematically illustrating an example of an output waveform of the high frequency power supply at the time of a shift between two processing steps respectively conducted before and after the shift while continuing a pulse output in the conventional technique. In FIG. 1, a shift between the processing steps is conducted to change over the output of the high frequency power supply from a pulse output of high output intensity, a low duty ratio, and a high pulse frequency to a pulse output of low output intensity, a high duty ratio, and a low pulse frequency.
In FIG. 1, reference numeral 101 illustrates an ideal shift of processing step in which the output intensity, duty ratio, and pulse frequency are changed over at the same time. Reference numerals 102 to 105 illustrate output waveforms at the time of a shift of processing step in a case where deviations occur in changeover instructions of the output intensity, duty ratio, and pulse frequency. As for causes of such occurrence of deviations in changeover instructions at the time of the shift of processing step, a difference in time constant between output control of the high frequency power supply and changeover of an external trigger pulse signal, a deviation in timing of an instruction from the controller to the high frequency power supply, and variations of delay times of relays, electronic components, and the like within the high frequency power supply are conceivable.
Comparing 102 to 105 in FIG. 1 with 101, a period of high output intensity becomes long in any output waveform. If high frequency power for plasma generation is applied with output intensity as illustrated I 102 to 105, plasma that is high in electron temperature and degree of dissociation is generated and it becomes impossible to maintain suitable ions and a suitable radical ratio. As a result, there is a fear that the etching speed will become low and the work shape will deteriorate. In the same way, if high frequency power for ion drawing bias application is applied with output intensity as illustrated in 102 to 105 in FIG. 1 in a state in which plasma is generated, there is a fear that the semiconductor wafer will be damaged by dielectric breakdown caused by the electron shading effect in addition to deterioration of the selection ratio.
As a conventional technique for controlling an output of the high frequency power supply at the time of such a shift of processing step, a technique disclosed in JP-2004-79600-A is known. The conventional technique prevents output of a continuous wave (CW) with intensity of setting or more from occurring by suitably controlling changeover instruction timing of output intensity and an output mode.
In the above-described conventional technique, the following points are not considered sufficiently and consequently problems occur.
That is, control on the changeover instruction timing of the output intensity and output mode in JP-2004-79600-A cope with only the time of changeover of the output mode. If high frequency power for plasma generation is applied in the output intensity when changeover to an output different in the output intensity, pulse frequency, and the duty ratio is conducted while the pulse output mode is continued as illustrated in FIG. 1, therefore, plasma that is high in electron temperature and degree of dissociation is generated, and suitable ions and a radical ratio. There is a fear that the etching speed will become lower and the work shape will deteriorate.
In addition, there is a fear that the selection ratio will deteriorate and the semiconductor wafer will be damaged by dielectric breakdown caused by the electron shading effect. A consequent problem that the yield of sample processing is hampered is not considered in the above-described conventional technique.